1. Field of the Invention
The present invention relates to an optical channel power equalizer for equalizing per-channel power levels of a multi-channel optical signal.
2. Description of the Related Art
Since a conventional multi-wavelength optical transmission system is operated by a point-to-point transmission method, multi-channel optical signals in the system are transmitted via the same transmission line. Consequently, they experienced the same transmission characteristics and optical losses. On the other hand, a current multi-wavelength optical transmission system is changed to adopt a point-to-multipoint transmission method that employs an optical add/drop multiplexer and an optical cross connector. When optical signals transmitted via different paths are switched per channel or link in the multi-wavelength optical transmission system, the per-channel power levels of the switched multi-channel optical signals are different from each other. In order to guarantee the transmission performance of the system, the per-channel power levels of the multi-channel optical signal should be equalized to a predetermined value before they are multiplexed into an optical signal.
As conventional methods for equalizing optical power levels per channel in the multi-wavelength optical transmission system, there may be various methods using tunable acousto-optical filters or photo detectors detecting each channel. However, it is difficult to precisely measure the per-channel power levels of the multi-channel optical signal using these methods. Also, when using the photo detectors, the number of photo detectors increases according to the increase of the number of channels. It is therefore hard to implement the method of employing the photo detectors, as the system capacity increases.